Control strategy for an electric machine in a vehicle

ABSTRACT

A hybrid-electric vehicle method of controlling a hybrid electric vehicle is provided. The vehicle includes a traction battery, at least two electric-machines, and a controller. The controller is configured to, in response to a faulted condition one of the electric-machines during a drive cycle, command the other of the electric-machines to function in a mode in which torque output is restricted to a threshold value that depends on a voltage of the battery to maintain vehicle propulsion during the drive cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional Application No.61/695,666 filed Aug. 31, 2012, the disclosure of which is incorporatedin its entirety by reference herein.

TECHNICAL FIELD

The present disclosure relates to a system for controlling an electricmachine in an electric vehicle.

BACKGROUND

Battery electric vehicles (BEVs) include a fraction battery that isrechargeable from an external electric power source and powers theelectric machine. Hybrid electric vehicles (HEVs) include an internalcombustion engine, one or more electric machines, and a traction batterythat at least partially powers the electric machine. Plug-in hybridelectric vehicles (PHEVs) are similar to HEVs, but the traction batteryin a PHEV is capable of recharging from an external electric powersource. These vehicles are examples of vehicles that are capable ofbeing at least partially driven by an electric machine.

In these vehicles, if a failure of a component necessary for electricpropulsion is detected, several actions may be necessary to ensure thesafety of the vehicle occupants. Since shutdown of the entire vehiclemay be undesirable, limited operation strategy (LOS) modes can beimplemented to enable the operator of the vehicle to continue to drivewhile individual components are disabled.

SUMMARY

In one embodiment of the disclosure, a vehicle is provided including afraction battery, at least two electric-machines, and a controller. Thecontroller is configured to, in response to a faulted condition one ofthe electric-machines during a drive cycle, command the other of theelectric-machines to function in a mode in which torque output isrestricted to a threshold value that depends on a voltage of the batteryto maintain vehicle propulsion during the drive cycle.

In another embodiment, the vehicle further includes at least onevariable voltage converter (VVC) and an inverter operatively arrangedwith at least one of the electric-machines. In response to the faultedcondition during the drive cycle, the controller is further configuredto temporarily disable the other of the electric-machines. Thecontroller also commands the VVC to function in a mode in which voltagefrom the inverter is routed to the battery while the other of theelectric-machines is disabled.

In another embodiment, the threshold value further depends on a speed ofthe other of the electric-machines.

In another embodiment, the at least one controller is further configuredto re-enable the faulted electric-machine during the drive cycle.

In another embodiment, wherein the other of the electric-machines istemporarily disabled for no more than 500 milliseconds.

In another embodiment, the vehicle further includes at least oneinverter coupled to the electric-machines, wherein the fault conditionoccurs on one the electric-machines or the at least one inverter.

In one embodiment of the disclosure, a method of controlling ahybrid-electric vehicle is provided. The method disables a firstelectric-machine in response to on a fault condition. A secondelectric-machine is commanded to function in a mode in which torqueoutput is restricted to a threshold value that depends on a voltage of atraction battery in order to maintain vehicle propulsion by the secondelectric machine during the drive-cycle.

In another embodiment, the method further includes re-enabling the firstelectric-machine during the drive-cycle.

In another embodiment, disabling the first electric-machine sets thefirst electric-machine to at least one of a one of a temporary disabledmode, permanently disabled mode or zero-torque mode.

In another embodiment, disabling the first electric-machine providessubstantially zero power flow to the first electric-machine.

In another embodiment, the method further includes temporarily disablingthe second electric-machine. A variable voltage converter is commandedto function in a mode in which high voltage from a high voltage electricconnection is routed to the battery while the second electric-machinesis disabled in order to quickly dissipate high voltage in response tothe fault condition.

In another embodiment, the second electric-machines is temporarilydisabled for less than 500 milliseconds.

In one embodiment of the disclosure, a method of controlling ahybrid-electric vehicle is provided. The method detects a faultcondition on a first electric-machine. The first electric-machine isdisabled in response to the fault condition. A second electric-machineis disabled temporarily in response to on the fault condition. Avariable voltage converter (VVC) is to a bypass mode in response to onthe fault condition, wherein the bypass mode dissipates high voltagepower. After a threshold time, the VVC is re-enabled and the seconddevice is set to a torque limiting mode to maintain propulsion by thesecond electric machine during the drive-cycle.

In another embodiment, the method further includes setting a maximumtorque for the second electric-machine based on an available batteryvoltage.

In another embodiment, the threshold time less than 500 milliseconds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hybrid-electric vehicle according toone embodiment of the disclosure;

FIG. 2 is a block diagram illustrating an example of a control system ofthe vehicle of FIG. 1;

FIG. 3 is a schematic illustration of a portion of the vehicle of FIG.1;

FIG. 4 is a schematic illustration of a Variable Voltage Converter (VVC)of FIG. 3;

FIG. 5 is a flow chart of an algorithm implemented in a control systemof the vehicle of FIG. 1 according to one embodiment of the disclosure;

FIG. 6 is a flow chart of another algorithm implemented in the controlsystem of the vehicle of FIG. 1 according to one embodiment of thedisclosure; and

FIG. 7 is a flow chart of another algorithm implemented in the controlsystem of the vehicle of FIG. 1 according to one embodiment of thedisclosure;

FIG. 8 is a flow chart of another algorithm implemented in the controlsystem of the vehicle of FIG. 1 according to one embodiment of thedisclosure;

FIG. 9 is a flow chart of another algorithm implemented in the controlsystem of the vehicle of FIG. 1 according to one embodiment of thedisclosure; and

FIG. 10 is a flow chart of another algorithm implemented in the controlsystem of the vehicle of FIG. 1 according to one embodiment of thedisclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

Referring to FIG. 1, a hybrid-electric vehicle 10 is illustrated havinga power-split powertrain. A vehicle control system 12 is provided, andcan generally be referred to as a controller. The vehicle control system12 controls the power distribution in the powertrain or driveline of thevehicle 10.

The vehicle 10 includes a traction battery 14. The battery 14 has atwo-way electrical connection, such that the battery 14 receives andstores electric energy through regenerative braking, for example. Thebattery 14 also supplies the energy to an electric machine, such as anelectric traction motor 16.

Although the control system 12 of the vehicle 10 is illustrated in FIG.1 as a single controller, such a control system can include more thanone controller, as desired. For example, a separate battery controlmodule can directly control the battery 14. Furthermore, a separatemotor control module can be directly connected to the motor 16 and tothe other controllers in the vehicle 10. It should be understood thatall contemplated controllers in the vehicle 10 can be referred to as a“controller”, and the vehicle control system 12 is not necessarilylimited to only one controller. Separate additional controllers andtheir hierarchy will be described in more detail FIG. 2.

An inverter 15 is provided to converts direct current (DC) from thebattery into alternating current (AC) for powering the electric machine.The inverter 15 may also selectively enable/disable electrical flow fromthe battery 14 to the motor 16. Alternatively, during regenerativebraking, the inverter 15 converts AC from the electric machine into DCsuch that electric power is stored in the battery 14.

An internal combustion engine 18 is also a power source for the vehicle10. The vehicle control system 12 controls the operation of engine 18.Both the motor 16 and the engine 18 are capable of powering atransmission 20 that ultimately delivers torque to the wheels of thevehicle 10.

The engine 18 delivers power to a torque input shaft 22 that isconnected to a planetary gear set 24 via a one way clutch. The inputshaft 22 powers the planetary gear set 24. The planetary gear set 24includes a ring gear 26, a sun gear 28, and a planetary carrier assembly30. The input shaft 22 can be driveably connected to the carrierassembly 30 which, when powered, can rotate the ring gear 26 and/or thesun gear 28. The sun gear 28 can be driveably connected to a generator32. The generator 32 may be engaged with the sun gear 28, such that thegenerator 32 may either rotate with the sun gear 28, or can bedisengaged so that the generator 32 does not rotate with the sun gear28. Like the motor 16, the generator 32 may be referred to as anelectric machine which, when utilized in other vehicle powertrainconfigurations, is capable of both generating electric power andproviding motive power.

When the engine 18 is driveably coupled to the planetary gear set 24,the generator 32 generates energy as a reactionary element to theoperation of the planetary gear set 24. Electric energy generated fromthe generator 32 is transferred to the battery 14 through electricalconnections 36. The battery 14 also receives and stores electric energythrough regenerative braking, in known fashion. The battery 14 suppliesthe stored electric energy to the motor 16 for operation. The portion ofthe power delivered from the engine 18 to the generator 32 may also betransmitted directly to the motor 16. The battery 14, motor 16, andgenerator 32 are each interconnected in a two-way electric flow paththrough electrical connections 36. The vehicle control system 12controls the components in the powertrain to provide proper torquedistribution to the wheels.

It should be understood that the motor 16 and the generator 32 can bothbe referred to as an electric machine. Each electric machine can operateas a generator by receiving torque from the engine 18 and supplying ACvoltage to the inverter 15, whereby the inverter 15 converts the voltageinto DC voltage to charge the battery 14. Each electric machine can alsooperate as a generator by utilizing regenerative braking to convert thebraking energy of the vehicle into electric energy to be stored in thebattery 14. Alternatively, each electric machine can operate as a motorwhereby the electric machine receives power from the inverter 15 and thebattery 14 and provides torque through transmission 20 and ultimately tothe wheels 58.

The inverter 15 selectively powers the motor 16 and the generator 32.The inverter 15 can include a motor inverter for selectively disablingthe motor 16, and a generator inverter for selectively disabling thegenerator 32.

The vehicle 10 can also include a variable voltage converter (VVC) 60,or also referred to as a boost converter, for varying voltage betweenthe battery 14 and the motor 16 and the generator 32. The VVC 60 is usedto boost the battery 14 voltage to a higher voltage. The higher voltagein a hybrid-electric drivetrain system can be used for multiple purposessuch as torque capability optimization for electric machines, systemloss optimization, and well other hybrid-electric system optimization.The VVC 60 allows the vehicle 10 to use a smaller battery pack withlower voltage while maintaining the functionally associated with thehigher voltage. A smaller battery pack may have advantages such as lowercost, smaller size and less packaging restraints, for example. The VVC60 will be described in more detail in FIG. 3 and FIG. 4.

The vehicle 10 may be powered by the engine 18 alone, by the engine 18and generator 32 alone, by the battery 14 and motor 16 alone, or by acombination of the engine 18, battery 14, motor 16 and generator 32. Ina mechanical drive mode, or a first mode of operation, the engine 18 isactivated to deliver torque through the planetary gear set 24. The ringgear 26 distributes torque to step ratio gears 38 comprising meshinggear elements 40, 42, 44, and 46. Gears 42, 44, and 46 are mounted on acountershaft, and gear 46 distributes torque to gear 48. Gear 48 thendistributes torque to a torque output shaft 50. In the mechanical drivemode, the motor 16 may also be activated to assist the engine 18 inpowering the transmission 20. When the motor 16 is active in assisting,gear 52 distributes torque to gear 44 and to the countershaft.

In an electric drive mode (EV mode), or a second mode of operation, theengine 18 is disabled or otherwise prevented from distributing torque tothe torque output shaft 50. In the EV mode, the battery 14 powers themotor 16 to distribute torque through the step ratio gears 38 and to thetorque output shaft 50. The torque output shaft 50 is connected to adifferential and axle mechanism 56 which distributes torque to tractionwheels 58. The vehicle control system 12 controls each of the battery14, motor 16, engine 18 and generator 32 to distribute torque to thewheels 58 in either the mechanical drive mode or the EV mode accordingto driver torque demands.

As previously described, there are two power sources for the driveline.The first power source is the engine 18, which delivers torque to theplanetary gear set 24. The other power source involves only the electricdrive system, which includes the motor 16, the generator 32 and thebattery 14, where the battery 14 acts as an energy storage medium forthe generator 32 and the motor 16. The generator 32 may be driven by theplanetary gear set 24, and may alternatively act as a motor and deliverpower to the planetary gear set 24.

It should be understood that while a power-split powertrain isillustrated in the vehicle 10, the vehicle 10 can include many otherconfigurations. As such, it is contemplated that individual componentsof the powertrain may differ to suit various particular applications.For example, in another configuration that does not include a planetarygear set 24, an electric machine (motor/generator) can be provided tooperate as a generator by receiving torque from the engine orregenerative braking, while the same electric machine can also operateas a motor by receiving power from the traction battery and providingtorque through the transmission. Other vehicle configurations of vehiclepowertrains and implementations of electric machines are contemplated,and are therefore considered to be within the scope of the presentdisclosure.

Referring to FIG. 2, a block diagram illustrating a vehicle controlsystem 12 within the vehicle 10 is shown. A driver inputs a request 62,such as pressing the accelerator to input an acceleration request orpressing the brake pedal to input a braking request, for example. Thedriver inputs 62 are received by a vehicle system controller (VSC) 64.The VSC 64 processes these driver inputs 62 and communicates commandsthroughout the vehicle 10.

The vehicle control system 12 may be electrically connected to withvarious subsystems in the vehicle 10 and acts as an overall control ofthe vehicle 10. The VSC may be electrically connected to and communicatewith various subsystems through a vehicle network 65. The vehiclenetwork 65 continuously broadcasts data and information to thevehicle-based systems. The vehicle network 65 may be a controlled areanetwork (CAN) bus used to pass data to and from the VSC 64 and othervarious controllers or subsystems or components thereof. For example, asshown in FIG. 2, the VSC 64 can be connected to a hybrid control unit(HCU) 66, a battery control module (BCM) 72 and an engine control unit(ECU) 68 through the vehicle network 65.

The HCU 66 that controls the hybrid-specific components in the vehicle10, such as the motor 16, the generator 32, the battery 14 and/or theinverter 15. The HCU 66 is communicatively connected to the ECU 68 suchthat the HCU 66 may command the ECU 68 to control the engine 18 invarious manners. A battery control module (BCM) 72 may also communicatewith the HCU 66. The BCM 72 may receive commands from the HCU 66 andcontrols the power distribution of the battery 14.

The HCU 66 is also communicatively connected to a motor/generatorcontrol unit (MGCU) 70. The MGCU 70 communicates with the HCU 66 througha Single Peripheral Interface (SPI) 71. SPI 71 is four-wire serial bus.The SPI 71 is an extremely simple hardware interface and is not limitedto any maximum clock speed, thus enabling potentially high throughput.The MGCU 70 receives commands from the HCU 66 and controls both themotor 16, the generator 32, and VVC 60. As further illustrated in FIG.2, the MGCU 70 is communicatively connected to inverter controls 74. Themotor/generator inverter controls 74 receive commands from the MGCU 70and open and close switches within the inverter 15 to enable and disablepower flow to and from the electric machines.

Previous hybrid-electric vehicles used one control module to control themotor, generator and VVC. Within the control module, one microcontrollerwas used to control the motor and another microcontroller to control thegenerator while a third controller controlled the VVC. However, it wasfound to be difficult to control the VVC when it was separated from themotor/generator and it was found to be too slow in conveying informationfrom the motor or generator to the VVC controls in the HCU. Therefore,it is advantageous to control the VVC, the motor, the generator and therespective inverters from one controller such as the MGCU shown in FIG.2.

A hierarchy of controllers is thus provided in the illustration shown inFIG. 2. Other hierarchies of controllers are contemplated withoutdeviating from the scope of the present disclosure. For example, the VSC64 may directly communicate with the MGCU 70 without the presence of anHCU 66. Other configurations are contemplated that would be beneficialfor different particular vehicle architectures.

The vehicle control system 12 controls each of the controllers,according to requested torque and power demands. It should again beunderstood that more or less controllers than those described herein arecontemplated, and one or more of these controllers can communicativelycooperate to accomplish certain tasks. Any and all of these controllersor combination thereof can simply be referred to as a “controller”.

Referring now to FIG. 3 and FIG. 4, a schematic diagram of a portion ofhybrid-electric vehicle 10 and vehicle control system 12 is described inmore detail. As previously discussed, the VVC 60 is communicativelyconnected and controlled by the MGCU. Further, the VVC 60 is connectedto the motor/generator inverter controls 74. Specifically, the VVC 60 isused to boost the battery 14 voltage to a higher level voltage in a HEVdrivetrain system for multi-purposes such as, but not limited to, torquecapability optimizations for electric machines and system lossoptimization.

The battery 14 is connected to the VVC 60 along an input side 76. Thebattery 14 supplies a low voltage to the VVC 60. The VVC 17 then booststhe low voltage from the battery 14 into a higher voltage and outputsthe higher voltage to an output side 78. The output side 78 of the VVC60 is supplying the high voltage to the high voltage bus 36 for use bythe inverter 15 and subsequently the motor 16 and generator 32. As shownin FIG. 3, the motor 16 and generator 32 may each have a separateinverter 15. While the VVC 60 is described as having an input side andan output side, it should be noted that in a motoring mode, the pathflows from the battery through the VVC to the high voltage bus.Conversely, in a regeneration mode, the path is reversed.

A sensor 80 is located between the battery 14 and VVC to measure to thevoltage signal along the input side 76 of the VVC 60. More specifically,the sensor 80 provides a voltage signal indicating the voltage from thebattery 14. A second sensor 82 is located along the output side 78between the VVC 60 and the inverters 15. The sensor 82 provides a signalindicating voltage from the high voltage bus 36. The sensors 80, 82provide a signal indicative of the measured voltage along the input side76 and the output side 78 respectively. During normal operatingconditions, the measured voltage signal is from the sensors 80, 82 iswithin an appropriate specified range. However, if the measured voltagesignal from the sensors deviates from the appropriate specified range,this may indicate that a fault has occurred or that one of the sensors80, 82 has failed.

Referring to FIG. 4, a schematic diagram of the VVC 60 circuitry isillustrated. The VVC 60 generally consists of an inductor 84, two powerswitches 86 and 88, and related gate drive circuits 90 as shows in FIG.4. The two power switches 86, 88 are composed of an insulated-gatebipolar transistor 92, 94 and an anti-parallel diode 96, 98. As shown inFIG. 4, the switches are arranged as an upper switch 86 and lower switch88.

The circuitry arrangement of the VVC allows for bi-directional powerflow depending on the vehicle requirements, such as motoring orregeneration, for example. For example, when the upper switch 86 isclosed and the lower switch 88 is open, power flows in one directionthrough the anti-parallel diode 96. Similarly, if the upper switch 86 isopen and the lower switch 88 is closed, power flows in one directionthrough the anti-parallel diode 98. However, when both the upper switch86 and lower switch 88 are closed, bi-directional power flow occurs andgenerates voltage boost. The boost voltage generated is output to theinverter 15 which controls the motor 16 and generator 32. As discussedpreviously, by allowing voltage boost through the VVC 60, the vehiclemay be able to have a smaller battery pack, thereby saving cost, andbattery packaging space, for example.

Certain fault conditions can be detected by one or more of thecontrollers that may indicate a fault in one of the powertraincomponents, such as the motor 16, the generator 32, the VVC 60 or theinverter 15. When a fault in one of the components is detected, alimited operation strategy (LOS) can be implemented to enable theoperator of the vehicle to continue to drive while certain individualcomponents are disabled. This prevents complete shutdown of the vehicle10, which can be undesirable to drivers. The fault conditions that maycause the vehicle 10 and/or vehicle control system 12 to enter a LOSmode can include temperature, current and/or voltage of a powertraincomponent being outside an acceptable threshold. A fault condition maybe caused by a transient event and may be only temporary; however, areading of a value outside a threshold can cause the vehicle controlsystem 12 to command an individual shutdown of that component, whilecommanding a LOS mode to allow the operator of the vehicle 10 tocontinue driving.

Referring now to FIG. 5, one embodiment of the LOS mode is illustratedat 100. A diagnostic is performed on each of the motor 16, the generator32, the VVC 60 and the inverter 15 associated with each of the electricmachines. The diagnostic determines if the LOS mode is necessary suchthat a temporary disabling of that component should be commanded. TheMGCU 70 begins performing the diagnostic, as represented by block 102.Next, as represented by block 104, it is determined whether or not afault condition exists in the motor and/or motor inverter. If there issuch a fault condition, an LOS counter is increased, as represented byblock 106. The LOS counter can be a single digit counter oridentification means. Once the LOS counter is increased by one, asrepresented by block 108, a motor temporary disablement flag is flaggedas TRUE. The motor is requested to be disabled, as represented by block110. The motor may be disabled by opening switches in the motor inverteror opening another switch associated with the motor.

If there is no fault condition in the motor and/or motor inverter, it isthen determined whether the LOS counter is greater than zero, asrepresented by block 112. If the LOS counter is not greater than zero,the motor temporary disablement flag is flagged as FALSE, and the motoris requested to be enabled, or continued to be enabled, as representedby block 116.

However, if the LOS fault counter is greater than zero, then the LOScounter is decremented or decreased, as represented by block 118. Afterthe LOS counter has been reduced, it is determined whether the faultcounter has reached zero, as represented by block 120. If the LOScounter is zero, then the method proceeds to set the flag for motordisablement to FALSE, as represented by block 114, and the motor isrequested to be enabled, or continued to be enabled, as represented byblock 116. If the fault counter remains greater than zero, then themethod proceeds again to disable the motor, as represented by blocks108, 110. Finally, the TRUE and FALSE flags are sent to the vehiclecontrol system, as represented by block 122. Based on the informationsent to the vehicle control system, the vehicle can act according to thedescription provided with reference to FIG. 6.

By requiring that the fault counter is equal to zero, as represented byblock 120, the control system ensures that even if it is determined thatthere is no fault condition in the motor and/or the motor inverter, themotor will continue to be temporarily disabled for a period of time ifthe LOS fault counter is still above zero. This allows the diagnostic tocontinue to run multiple times while reducing the LOS fault counter eachtime the diagnostic is run, until the counter reaches zero. Multiplechecks of the motor and/or the motor inverter are therefore conductedwhile the motor is disabled before re-enabling the motor if no faultcondition is detected.

The diagnostic performed by the MGCU works to temporarily disable themotor in the event a fault condition is detected. While the motor istemporarily disabled, the vehicle operates in a temporarily reducedpower mode. However, if the fault condition only exists for a shortamount of time (e.g., under 1 second), the LOS mode be discontinued andthe motor will be re-enabled quickly, thus reducing the disturbancesfelt by the operator of the vehicle. It should be understood that theentire diagnostic can be accomplished in less than one second, such asin twenty micro-seconds, and thus the time the motor is temporarilydisabled may not be detected by the operator of the vehicle.

As shown in FIG. 5, the LOS mode 100 and the performing of diagnosticsoperation, as represented by block 102, is performed for both thegenerator and the VVC as well as the motor. The diagnostics areaccomplished for the motor, the generator, the associated inverter andthe VVC generally simultaneously such that a check for fault conditionsis continuous in each component. The MGCU can thus temporarily disableany or all of the motor, the generator, or the VVC. It is contemplatedthat the diagnostics can also be accomplished for other components, suchas the engine.

FIG. 6 illustrates a flowchart 200 of another embodiment of the LOS modeimplemented by a controller, or the vehicle control system. Aspreviously described, the MGCU sets a flag for either TRUE or FALSE totemporarily disable or enable the motor, as represented by blocks 108and 114 respectively. The TRUE and/or FALSE flags are received by thevehicle control system from the MGCU, as represented by block 202. Ifthe flag is FALSE, then the vehicle control system commands the MGCU toreturn to the diagnostic check 102, as represented by block 204.

However, if the flag is TRUE, then a determination is made as to whetherthe motor has been temporarily disabled for at least a threshold time,as represented by block 206. If the motor has been disabled for at leastthe threshold time, then the motor can be permanently disabled for thecurrent key cycle, as represented by block 208. In one embodiment, thethreshold time may be approximately one second, such that the motor willbe permanently disabled during the current key cycle if it has beentemporarily disabled for at least one second. However, any suitablethreshold time is contemplated and the threshold time may be variabledepending on other factors. A key-cycle may also be referred to as adrive-cycle or power-cycle and is the time from when the vehicle ispowered on, i.e. key-on, until the vehicle is shutdown during a key-off.During a new key cycle, the motor, or any faulted device such as the VVCor inverter, can be re-enabled, as will be described with reference toFIG. 7.

The algorithms described with reference to FIG. 5 and FIG. 6 provide fora diagnostics check of the motor, the generator, the VVC, or any otherpowertrain component. In short, if the particular powertrain componentis detected to be operating under a fault condition, that component istemporarily disabled. Diagnostics continuously run on that componentwhile it is temporarily disabled. If the component recovers from itsfault condition or the fault was transient so that the component canoperate under normal conditions within the time threshold, the componentcan be re-enabled. If, however, the component fails to recover from itsfault condition within the time threshold, the component is permanentlydisabled during the current key cycle, and can only be re-enabled upon anew key cycle (e.g., turning the vehicle off and on).

FIG. 7 illustrates a flowchart 300 of another embodiment of the LOS modeimplemented by a controller, or the vehicle control system. Asrepresented by block 302, the vehicle is requested to start, and a newkey cycle is commanded. Initially the electric machines, including themotor, generator, as well as the VVC are disabled. A series of pre-startsafety checks before initializing of the vehicle.

For example, the vehicle control system checks that the current sensorzeroing is complete, as represented by block 304. The current sensorzeroing must be complete throughout the electric machines. The currentsensors must have a zeroed reading while the current is zero in order tohave accurate readings for when the current spikes during startup. Next,a self-test of the VVC is accomplished, as represented by block 306. TheVVC self test ensures that any faults within the VVC are detected andresolved. Also, a determination is made as to whether there are anytorque failures present, as represented by block 308. In other words,the available power and/or torque of the electric machines must beevaluated to determine whether any requested torque can be fulfilled bythe electric machines.

The duty cycle commands provided to the electric machine are disabled orreset by the controller, as represented by block 310. Resetting the dutycycle puts the electric machines in a safe mode, thus protecting thehardware. Only after the fault conditions are removed can the duty cyclecommands be re-enabled, allowing the electric machine to be safelycontrolled. This is considered to be a “soft restart” in which no newkey cycle necessary, rather than a “hard restart” in which the vehiclemust be shut down. Finally, as represented by block 312, any faultspresent in the hardware are determined before enabling the vehicle tostart.

Once the pre-start safety checks are successfully completed, the vehiclestarts and the electric machines can begin, as represented by block 314.The electric machines are also fully enabled, and the vehicle can bedriven.

During operation of the vehicle, the diagnostic algorithms describedwith reference to FIG. 5 and FIG. 6 are accomplished and represented asblock 316. The electric machines are continuously checked for faultssuch that any of them can be temporarily disabled, according to themethods previously described.

If a request to disable any of the electric machines is determined atblock 316, the electric machine is disabled, as represented by block318. In order to re-enable the electric machine, the controllers in thevehicle must accomplish a series of safety checks and safety processesbefore re-enabling the electric machine again at block 314. The safetychecks and processes allow the vehicle to continue driving and theelectric machines to continue providing propulsion without having akey-cycle.

In one of the safety checks, as represented by block 320, the controllerdetermines whether a temporary disablement of the electric machine isstill being required, as previously described in reference to block 110of FIG. 5. If disabling in not being requested of the electric machines,the controller can determined whether any of the electric machines arerequested to be in a shutdown or permanent disablement mode, asrepresented by block 322. If the electric machines are not disabled, atorque fulfillment check is completed, as represented by block 324. Thetorque fulfillment check is similar to the check performed withreference to block 308.

Next, a power limiting and balancing check is completed, as representedby block 326. In this check, the controller may determine whether aprocess is underway in which electrical power is limited to one of theelectrical machines or that one of the electric machines does not havepower or torque limit much greater than the other electrical machine.The power limiting mode will be described in more detail in FIG. 8.Finally, an over-current check is accomplished as represented by block328. The over current check determines whether any electric machine issupplied with or is outputting a current value over a given threshold.If all of the safety checks are satisfactory, the prestart/re-enabledchecks at are completed starting again at block 302, until the disabledelectric machine is re-enabled at block 314.

FIG. 8 illustrates a flowchart 400 of another embodiment of the LOS modeimplemented by a controller, or the vehicle control system. FIG. 8describes a LOS mode where a power limiting mode is implemented when afault condition is detected on one of the electric machines. In previoushybrid-electric vehicles, failures or fault conditions in ahybrid-electric vehicle drivetrain were difficult to mitigate withoutreducing vehicle performance while driving or stopping the vehiclecompletely and then required a key cycle to resume partial operation. Akey cycle was necessary to properly maintain power balance with thefaulted device. In a hybrid electric transmission, when a failure isdetected on one of the devices, such as an electric machine, takingaction on only the faulted device would result in a power imbalance andwould lead to unstable performance and additional control-relatedfaults.

To avoid power imbalance and unstable performance, flowchart 400 in FIG.8 describes the process where the vehicle enters the LOS mode uponfailure of one of the electric machines while driving, and continuing tooperate the hybrid electric drivetrain with the second electric machinewithout requiring a key cycle. The process described in flowchart 400allows the control system to quickly balance power when one of theelectric machines fails and allows the other electric machine tocontinue to provide propulsion to the vehicle.

Initially, as represented by block 402, the control system detects afailure in a first hybrid-electric drivetrain device and disables thedevice in response to the fault condition. The failure may occur in oneof the electric machines, or the associated inverters. In response tothe fault condition and the disabled device, the control systeminitiates a power limiting mode, as represented by block 404. Initially,the power limiting mode is conducted at a high speed execution rate. Thehigh speed rate may be an execution rate of 100 microseconds, forexample.

While still operating in a high speed execution rate, the control systemtemporarily disables the second device, as represented by block 406. TheVVC is also temporarily set to a bypass mode, as represented by block408. The bypass mode of the VVC allows the high voltage from theelectric machines to be quickly dissipated to the low voltage input sideof the VVC. A fault may also be displayed for the driver, in response tothe failure, as represented by block 410.

After a threshold time, the control system can initiate a power limitingmode at a lower speed execution rate, as represented by block 412. Thethreshold time may be as short as 20 milliseconds, or any suitablethreshold time that is enough time for the high voltage to dissipate sothat the devices are not threatened with over-voltage, which could causemore failures. The control system initiates the lower speed executionrate so that additional diagnostics can be performed.

Once the low speed power limiting mode is initiated, the control systemre-enables the second device that is not faulted. However, the seconddevice is re-enabled in a torque limited mode, as represented by block414. In the torque limited mode, torque on the functional device islimited on the functional device based on vehicle operation. The maximumtorque in the LOS mode is limited based on the following formula:

τ_(max)=(I _(max) ×V _(battery))/ω

In other words, the maximum torque in the LOS mode is limited based onthe maximum allowable current of the high voltage bus in LOS modemultiplied by the voltage from the battery divided by the speed of thesecond device. In one embodiment, the maximum allowable current in theLOS mode is a fixed value, such as 150 Amps. The battery voltage can bevariable.

Once the functional device is re-enabled in a functional mode, thecontrol system checks to determine if the first device is still faultedor disabled, as represented by block 416. If the first device is beingrequested to be disabled by the MGCU or the HCU, or continues to have afailure, a power limiting time counter is incremented, as represented byblock 420. However, if there is no fault and there is no disablementrequest from one of the controllers, the control system can exit thepower limiting mode, as represented by block 424. By exiting the powerlimiting mode, the control system also exits the low speed executionrate.

The control system then resets the power limiting time counter to zero,as represented by block 426. Once the power limiting time counter is setto zero and the LOS mode is cleared, the control system can alsore-enable the first and second devices, as represented by block 428.Re-enabling the devices includes exiting any torque limiting mode andreturning to normal function.

On the other hand, if the first device still has a faulted condition, orthe MGCU or HCU are requesting that the device is disabled or set to anLOS mode, the control system determines if the power limiting timecounter is greater than a threshold value, as represented by block 432.

If the power limiting time counter has exceeded a threshold value, thelow speed diagnostic mode is exited, as represented by block 434. Thenthe torque limiting mode is permanently maintained for the functionaldevice, as represented by block 436. By maintaining the torque limitingmode, the device is permanently disabled. In some embodiments, thedevice may only be permanently disabled until a new key-cycle of thevehicle. The device may be set as permanently disabled for severalreasons, including the method described in FIGS. 5-7.

FIG. 9 illustrates a flowchart 500 of another embodiment of the LOS modeimplemented by a controller, or the vehicle control system. A highvoltage battery signal, also known as the HVBATT signal, is received bythe controller, such as the MGCU, as represented by block 502. The highvoltage battery signal is measured by the sensor along the input side ofthe VVC. Based on the high voltage battery signal provided by thesensor, the controller determines if the high voltage battery signal isvalid, as represented by block 504. The high voltage battery signal isvalid if the signal is within an acceptable range.

If the HVBATT signal is valid, the controller continues to use then thehigh voltage battery signal, as represented by block 506, and the VVCmay function normally, such as where VVC provides voltage boost outputto the inverters and electric machines, as described in FIG. 3 and FIG.4.

However, if the high voltage battery signal is outside of the acceptablerange, the signal is determined to be invalid. When the high voltagebattery signal is invalid, then the signal is set to a fault condition,as represented by block 508. When the high voltage battery signal is setto the fault condition, the MGCU communicates with the HCU to determinewhether there is an alternative signal available to provide the highvoltage battery signal in order to prevent shut down or short of theelectric machines and the vehicle.

As previously described, the HCU is able to communicate through thevehicle network, such as CAN. For example, the HCU is able tocommunicate with the BCM on the vehicle network to receive an alternatebattery voltage signal from the BCM. The alternate battery voltagesignal from the BCM may be a measured voltage that is measured withinthe BCM. Alternatively, the alternate battery voltage signal may beinferred from other battery readings in the BCM or other vehicle systemcontrollers communicating with the vehicle network.

The MGCU determines if the alternate voltage signal provided from thevehicle network is valid, as represented by block 510. The alternatebattery voltage signal is considered to be a valid signal if the batteryvoltage is within an acceptable range. If the alternate battery voltagesignal from the BCM is considered to be valid, then the alternatebattery voltage signal is substituted in for the HVBATT, as representedby block 512. By using the alternate voltage signal in place of theHVBATT, the VVC can continue to operate normally, as represented byblock 514. In normal operation, the VVC can provide voltage boost fromthe battery voltage on the input side to the inverter and electricmachines on the output side. Therefore, with the on-the-fly substitutionof the alternate signals, the electric machines can continue to operatenormally, despite the faulted high voltage battery signal.

The vehicle may also display a fault for the driver, as represented byblock 516. The fault may be displayed as a wrench light informing thedriver of the fault condition. The fault condition in the high voltagebattery signal may be caused by a failure of the sensor. The display mayindicate that the sensor needs to be replaced.

If the MGCU determines that alternate signal is not valid, the controlsystem ignores the alternate signal, as represented by block 518. Thealternate signal may be invalid if it is beyond an acceptable range orthreshold value, for example. If the alternate signal is invalid, it mayindicate a secondary fault.

FIG. 10 illustrates a flowchart 600 of another embodiment of the LOSmode implemented by a controller, or the vehicle control system. A highvoltage battery bus signal, also known as the HVDC signal, is receivedby the controller, such as the MGCU, as represented by block 602. Thehigh voltage bus signal is measured by the sensor along the output sideof the VVC. Based on the high voltage bus signal provided by the sensor,the controller determines if the high voltage bus signal is valid, asrepresented by block 604. The high voltage battery signal is valid ifthe signal is within an acceptable range.

If the HVDC signal is valid, the controller continues to use the highvoltage bus signal, as represented by block 606, and the VVC mayfunction normally, such as where VVC provides voltage boost output tothe inverters and electric machines, as described in FIG. 3 and FIG. 4.

However, if the high voltage bus signal is outside of the acceptablerange, the signal is determined to be invalid. When the high voltage bussignal is invalid, then the signal is set to a fault condition, asrepresented by block 608. If the signal is considered invalid, the HVDCsignal is set to fault and LOS mode is implemented to maintain functionof the electric machines and to allow the operator of the vehicle tocontinue driving.

When the high voltage bus signal is set to the fault condition, the MGCUtries to substitute the high voltage battery signal, HVBATT from theinput side of the VVC, for the high voltage bus signal. The MGCUdetermines whether the high voltage battery signal is valid, asrepresented by block 610. It is contemplated that the controller maysubstitute any HVBATT signal, such as the high voltage battery signalmeasured by the sensor or the alternate battery voltage signal providedto the MGCU from CAN via the HCU, as discussed above in FIG. 9.

As discussed previously, the high battery voltage signal is consideredto be a valid signal if the battery voltage is within an acceptablerange. If the high voltage battery voltage signal is considered to bevalid, then the HVBATT, is substituted for the high voltage bus signal,as represented by block 612.

When using the high voltage battery signal in place of the high voltagebus signal, the VVC can continues to operate but the VVC is set to a LOSmode, as represented by block 614. In the LOS mode, the VVC is set to abypass mode. In the bypass mode, the VVC is disabled from providingvoltage boost, as represented by block 616. The vehicle may also displaya fault for the driver, as represented by block 618. Again, the faultmay be displayed as a wrench light informing the driver of the faultcondition. The fault condition in the high voltage bus signal may becaused by a failure of the sensor. The display may indicate that thesensor needs to be replaced.

If the MGCU determines that HVBATT signal is not valid, the controlsystem ignores the alternate HVBATT signal, as represented by block 620.The alternate signal may be invalid if it is beyond an acceptable rangeor threshold value, for example. If the alternate signal is invalid, itmay indicate a secondary fault in the HVBATT signal.

It should be understood that, while references have been made todisabling and enabling the motor, similar algorithms are contemplated toapply to the generator, the inverter and the VVC. In other words, if afault condition is present in any of the motor, the generator, theinverter or the VVC, the methods described above can apply to any ofthese components and other powertrain components.

The processes, methods, or algorithms disclosed herein can bedeliverable to/implemented by a processing device, controller, orcomputer, which can include any existing programmable electronic controlunit or dedicated electronic control unit. Similarly, the processes,methods, or algorithms can be stored as data and instructions executableby a controller or computer in many forms including, but not limited to,information permanently stored on non-writable storage media such as ROMdevices and information alterably stored on writeable storage media suchas floppy disks, magnetic tapes, CDs, RAM devices, and other magneticand optical media. The processes, methods, or algorithms can also beimplemented in a software executable object. Alternatively, theprocesses, methods, or algorithms can be embodied in whole or in partusing suitable hardware components, such as Application SpecificIntegrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs),state machines, controllers or other hardware components or devices, ora combination of hardware, software and firmware components.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. A vehicle comprising: a fraction battery; atleast two electric-machines; and at least one controller configured to,in response to a faulted condition one of the electric-machines during adrive cycle, command the other of the electric-machines to function in amode in which torque output is restricted to a threshold value thatdepends on a voltage of the battery to maintain vehicle propulsionduring the drive cycle.
 2. The vehicle of claim 1 further comprising atleast one variable voltage converter (VVC) and an inverter operativelyarranged with at least one of the electric-machines, wherein, inresponse to the faulted condition during the drive cycle, the controlleris further configured to: temporarily disable the other of theelectric-machines; and command the VVC to function in a mode in voltagefrom the inverter is routed to the battery while the other of theelectric-machines is disabled.
 3. The vehicle of claim 1 wherein thethreshold value further depends on a speed of the other of theelectric-machines.
 4. The vehicle of claim 1 wherein the at least onecontroller is further configured to re-enable the faultedelectric-machine during the drive cycle.
 5. The vehicle of claim 1wherein the other of the electric-machines is temporarily disabled forno more than 500 milliseconds.
 6. The vehicle of claim 1 furthercomprising at least one inverter coupled to the electric-machines,wherein the faulted condition occurs on one of the device or the atleast one inverter.
 7. A method of controlling a hybrid-electric vehiclecomprising: disabling a first electric-machine in response to on a faultcondition; and commanding a second electric-machine to function in amode in which torque output is restricted to a threshold value thatdepends on a voltage of a traction battery in order to maintain vehiclepropulsion by the second electric machine during a drive-cycle.
 8. Themethod of claim 7 further comprising re-enabling the firstelectric-machine during the drive-cycle.
 9. The method of claim 7wherein disabling the first electric-machine sets the firstelectric-machine to at least one of a temporary disabled mode,permanently disabled mode or zero-torque mode.
 10. The method of claim 7wherein disabling the first electric-machine provides substantially zeropower flow to the first electric-machine.
 11. The method of claim 7further comprising: temporarily disabling the second electric-machine;and commanding a variable voltage converter to function in a mode inwhich high voltage from a high voltage electric connection is routed tothe battery while the second electric-machine is disabled in order toquickly dissipate high voltage in response to the fault condition. 12.The method of claim 11 wherein the second electric-machines istemporarily disabled for less than 500 milliseconds.
 13. A method ofcontrolling a hybrid-electric vehicle comprising: detecting a faultcondition on a first electric-machine; disabling the firstelectric-machine in response to the fault condition; disabling a secondelectric-machine temporarily in response to on the fault condition;setting a variable voltage converter (VVC) to a bypass mode in responseto on the fault condition, wherein the bypass mode dissipates highvoltage power; and after a threshold time, re-enabling the VVC and thesecond electric machine to a torque limiting mode to maintain propulsionby the second electric machine during a drive-cycle.
 14. The method ofclaim 13 further comprising setting a maximum torque for the secondelectric-machine based on an available battery voltage.
 15. The methodof claim 13 wherein the threshold time less than 500 milliseconds.